Gradient- and sensitivity-enhanced heteronuclear multiple-quantum correlation spectroscopy

A gradient- and sensitivity-enhanced HMQC experiment has been developed. The sensitivity of the experiment is increased by factors of the square root of 2 and 2 over the conventional and gradient-enhanced HMQC experiments, respectively. This improvement is achieved by retaining both the x and the y magnetization components in the indirectly detected dimension. This experiment will be particularly useful in NMR studies of large biomolecules as the relaxation time of the multiple-quantum coherence is much longer than that of the single-quantum coherence in the slow motion limit.     

NMR spectroscopic elucidation of the structure of a glycerol teichoic acid-like O-specific polysaccharide of the bacterium Hafnia alvei strain PCM 1199

The structure of the acidic O-specific polysaccharide of a Gram-negative bacterium, H. alvei strain PCM 1199, was studied by NMR spectroscopy including two-dimensional correlation spectroscopy (COSY), total correlation spectroscopy (TOCSY), nuclear Overhauser effect spectroscopy (NOESY), 1H, 13C heteronuclear single-quantum coherence (HSQC), 1H, 13C heteronuclear multiple-bond correlation (HMBC), and one-dimensional 1H, 31P heteronuclear multiple-quantum coherence (HMQC) experiments. It was found that the polysaccharide contains D-galactose, 2-acetamido-2-deoxy-D-glucose, 4-acetamido-4,6-dideoxy-D-glucose, glycerol, and phosphate in the ratios 1:2:1:1:1, as well as O-acetyl groups in non-stoichiometric amounts. The polysaccharide is similar in structure to teichoic acids of Gram-positive bacteria and has the following structure of the repeating unit: 3)-beta-D-Galp-(1-->3)-alpha-D-GlcpNAc-(1-->3)-beta-D-Quip4NAc-(1- ->1)-Gro- 3-P-(O--> [formula: see text] beta-D-GlcpNAc [formula: see text] The O-specific polysaccharide of H. alvei PCM 1199 is structurally related to another teichoic acid-like O-specific polysaccharide of H. alvei PCM 1205 studied by us earlier.     

Structure of a neutral O-specific polysaccharide of the bacterium Proteus mirabilis O24

Lipopolysaccharide of the bacterium Proteus mirabilis O24 was found to have a neutral O-specific polysaccharide chain containing D-galactose, 2-acetamido-2-deoxy-D-glucose, and 2-acetamido-2-deoxy-D-galactose in ratios 1:2:1. On the basis of 1H- and 13C-NMR spectroscopy, including two-dimensional correlation spectroscopy (COSY), H-detected 1H, 13C heteronuclear multiple-quantum coherence (HMQC), and nuclear Overhauser effect spectroscopy (NOESY), the following structure of the branched tetrasaccharide repeating unit of the O-specific polysaccharide was established: -->3)-beta-D-GlcpNAc-(1-->4)-beta-D-GalpNAc-(1-->4)-beta-D-GlcpNAc-(1--> [formula: see text] beta-D-Galp.     

Proton NMR of Escherichia coli sulfite reductase: the unligated hemeprotein subunit

The isolated hemeprotein subunit of sulfite reductase (SiR-HP) from Escherichia coli consists of a high spin ferric isobacteriochlorin (siroheme) coupled to a diamagnetic [4Fe-4S]2+ cluster. When supplied with an artificial electron donor, such as methyl viologen cation radical, SiR-HP can catalyze the six electron reductions of sulfite to sulfide and nitrite to ammonia. Thus, the hemeprotein subunit appears to represent the minimal protein structure required for multielectron reductase activity. Proton magnetic resonance spectra are reported for the first time on unligated SiR-HP at 300 MHz in all three redox states. The NMR spectrum of high spin ferric siroheme at pH 6.0 was obtained for the purpose of comparing its spectrum with that of oxidized SiR-HP. On the basis of line widths, T1 measurements, and 1D NOE experiments, preliminary assignments have been made for the oxidized enzyme in solution. The pH profile of oxidized SiR-HP is unusual in that a single resonance shows a 9 ppm shift over a range of only 3 pH units with an apparent pK = 6.7 +/- 0.2. Resonances arising from the beta-CH2 protons of cluster cysteines have been assigned using deuterium substitution for all redox states. One beta-CH2 resonance has been tentatively assigned to the bridging cysteine on the basis of chemical shift, T1, line width, and the presence of NOEs to protons from the siroheme ring. The observed pattern of hyperfine shifts can be used as a probe to measure the degree of coupling between siroheme and cluster in solution. The cluster iron sites of the resting (oxidized) enzyme are found to possess both positive and negative spin density which is in good agreement with Mossbauer results on frozen enzyme. The NMR spectrum of the 1-electron reduced form of SiR-HP is consistent with an intermediate spin (S = 1) siroheme. Intermediate spin Fe(II) hemes have only been previously observed in 4-coordinate model compounds. However, the amount of electron density transferred to the cluster, as measured by the isotropic shift of beta-CH2 resonances, is comparable to that present in the fully oxidized enzyme despite diminution of the total amount of unpaired spin density available. Addition of a second electron to SiR-HP, besides generating a reduced S = 1/2 cluster with both upfield and downfield shifted cysteine resonances, converts siroheme to the high spin (S = 2) ferrous state.(ABSTRACT TRUNCATED AT 400 WORDS)     

Histological and histochemical study of hyperplastic and dysplastic lesions of the large intestine in Cebus Apella (primate) treated with 1,2-dimethylhydrazine

The optimization of the coherence transfers involved in five, seven and nine-quantum versions of the recently discovered MQMAS technique, is analysed numerically. Data reported in this paper may serve as starting parameters for the experiment set up. An analysis of the intensity and resolution given by each type of experiment is performed, which confirms the need to use very high rf fields for MQ transfers. It follows that five-quantum is achievable rather easily but the use of seven and nine-quantum MAS experiments becomes increasingly difficult due to the demand for high rf power and decreasing sensitivity. The advantages of using the z-filter MQMAS method with respect to a two-pulse sequence are analysed. The method for qualitatively and quantitatively interpret the MQMAS spectra is described. The nature of the spinning side bands along the multiple quantum dimension is explained. It is shown that the rotor synchronization can be conveniently used to eliminate these side bands, but only for 3QMAS experiments. The use of the multiple-quantum method in combination with static samples and VAS, DAS and DOR techniques is finally discussed.     

1H-15N NMR signal assignment and secondary structure of bacteriorhodopsin (1-231) in solution

15N-Labeled de-(232-248)-bacteriorhodopsin [BR(1-231)] was solubilized in 1:1 chloroform-methanol solvent mixture that contained 1.0 M 2HCO2N2H4 and mimic membrane medium. Resonances in the 1H-15N heteronuclear multiple-quantum coherence (HMQC) spectrum of BR (1-231) were assigned using the data of two- and three-dimensional NMR experiments. Of 117 cross-peaks present in the 1H-15N HMQC spectrum, 98 were assigned to residues in 1-75 and 193-231 segments of the protein. Almost all cross-peaks that correspond to the 76-192 segment were absent in the HMQC spectrum (except for six cross-peaks from the side chains and 14 cross-peaks from the backbone). Deuterium exchange rates of amide protons and cross-peaks of nuclear Overhauser effect helped to localize helices A (residues 8-30), B (residues 40-65), and G (residues 198-226). The periodicity in the rates of deuterium exchange of NH protons of helices A, B, and G was explained by the compact arrangement of these helices in the protein globule. The broadening of signals from six residues in helix G, which, according to the electron cryomicroscopy model of bacteriorhodopsin, is in contact with the NMR-unobservable bundle of helices CDEF, indicates specific interactions of the helices in BR(1-231). These data suggest that BR(1-231) solubilized in an organic medium has a spatial structure similar to that in the electron cryomicroscopy model of BR.     

Rapidly solidified prealloyed powders by laser spin atomization

A new technique, termed laser spin atomization, for the production of rapidly solidified prealloyed powders is described. The results of experiments involving the production of powders of two alloys, one based on Ni, the other on Ti, are presented. The powders have been characterized using light optical metallography, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Auger elec-tron spectroscopy, and these various observations are described.     

冷轧带钢粘结原因分析与解决

对冷轧带钢退火后出现的粘结的原因进行了分析,通过机理分析、生产统计和现场试验,提出了解决措施,应用后取得了良好的效果。     

Fe-heme conformations in ferric myoglobin

X-ray absorption near-edge structure (XANES) spectra of ferric myoglobin from horse heart have been acquired as a function of pH (between 5.3 and 11.3). At pH = 11.3 temperature-dependent spectra (between 20 and 293 K) have been collected as well. Experimental data solve three main conformations of the Fe-heme: the first, at low pH, is related to high-spin aquomet-myoglobin (Mb+OH2). The other two, at pH 11.3, are related to hydroxymet-myoglobin (Mb+OH-), and are in thermal equilibrium, corresponding to high- and low-spin Mb+OH-. The structure of the three Fe-heme conformations has been assigned according to spin-resolved multiple scattering simulations and fitting of the XANES data. The chemical transition between Mb+OH2 and high-spin Mb+OH-, and the spin transition of Mb+OH-, are accompanied by changes of the Fe coordination sphere due to its movement toward the heme plane, coupled to an increase of the axial asymmetry.     

Classification of amino acid spin systems using PFG HCC(CO)NH-TOCSY with constant-time aliphatic 13C frequency labeling

We have developed a useful strategy for identifying amino acid spin systems and side-chain carbon resonance assignments in small 15N-, 13C-enriched proteins. Multidimensional constant-time pulsed field gradient (PFG) HCC(CO)NH-TOCSY experiments provide side-chain resonance frequency information and establish connectivities between sequential amino acid spin systems. In PFG HCC(CO)NH-TOCSY experiments recorded with a properly tuned constant-time period for frequency labeling of aliphatic 13C resonances, phases of cross peaks provide information that is useful for identifying spin system types. When combined with 13C chemical shift information, these patterns allow identification of the following spin system types: Gly, Ala, Thr, Val, Leu, Ile, Lys, Arg, Pro, long-type (i.e., Gln, Glu and Met), Ser, and AMX-type (i.e., Asp, Asn, Cys, His, Phe, Trp and Tyr).     

Inference and Classification Learning of Abstract Coherent Categories.

Category learning research has primarily focused on how people learn to classify items using simple observable features. However, classification is only 1 way to learn categories. In addition, many concepts have an underlying coherence that explains the featural similarity among exemplars, such as abstract coherent concepts whose instances differ greatly on their observable features. In 3 experiments, the authors investigated how abstract coherent categories are acquired through 2 common means of category learning, classification and inference. Because inference promotes more focus on within-category information than does classification, they hypothesized that inference learning would lead to a better understanding of the underlying coherence of abstract coherent categories. All 3 experiments support this prediction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of coherence and relevance on shallow and deep text processing.

In 2 experiments, the authors examined the effects of coherence and relevance on shallow and deeper text processing, testing the hypothesis that enhancing the relevance of text segments compensates for breaks in local and global coherence. In Experiment 1, they found that breaks in local coherence had no effect on any outcome measures, whereas relevance enhanced deeper processing. In Experiment 2, they found that breaks in global coherence interfered with shallow processing, whereas relevance enhanced deeper processing. In addition, interactions revealed that relevance compensates for breaks in global coherence on measures of deeper processing. The compensation hypothesis was supported. One explanation for these results is that relevance enables readers to focus on salient information, which in turn can be used to repair serious coherence breaks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Infants' encoding of kinetic displays varying in relative coherence.

Two experiments were conducted to assess 3-month-old infants' processing of moving point-light displays depicting the biomechanical motions of a person walking. The displays were computer-generated and varied in stimulus coherence as measured by a version of coding theory. An infant-control habituation paradigm was used to measure both encoding and discrimination of the stimuli. Experiment 1 involved two point-light displays with identical absolute motions but different degrees of relative coherence. The results revealed that these two displays were discriminable and that encoding was systematically related to their relative coherence. Experiment 2 revealed that two new displays varying less in their coherence were also differentially encoded but were not discriminated. It was concluded that infants' processing of kinetic displays varies as a function of their relative coherence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The architecture of intuition: Fluency and affect determine intuitive judgments of semantic and visual coherence and judgments of grammaticality in artificial grammar learning.

People can intuitively detect whether a word triad has a common remote associate (coherent) or does not have one (incoherent) before and independently of actually retrieving the common associate. The authors argue that semantic coherence increases the processing fluency for coherent triads and that this increased fluency triggers a brief and subtle positive affect, which is the experiential basis of these intuitions. In a series of 11 experiments with 3 different fluency manipulations (figure-ground contrast, repeated exposure, and subliminal visual priming) and 3 different affect inductions (short-timed facial feedback, subliminal facial priming, and affect-laden word triads), high fluency and positive affect independently and additively increased the probability that triads would be judged as coherent, irrespective of actual coherence. The authors could equalize and even reverse coherence judgments (i.e., incoherent triads were judged to be coherent more frequently than were coherent triads). When explicitly instructed, participants were unable to correct their judgments for the influence of affect, although they were aware of the manipulation. The impact of fluency and affect was also generalized to intuitions of visual coherence and intuitions of grammaticality in an artificial grammar learning paradigm. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relative inhibition following the encoding of bridging and predictive inferences.

Inferences that maintained text coherence and inferences about predictable events were examined within a word recognition paradigm previously used in investigations of anaphor resolution. Although relative facilitation has been found for explicit targets involved in anaphoric inferences, in Exp 1, relative inhibition was found for explicit targets involved in inferences that established local coherence. Exp 2 demonstrated that this relative inhibition effect was specific to inference-related explicit targets. In Exp 3, recognition instructions that allowed participants to respond positively when a target had been read or thought about eliminated the inhibition effect, supporting a source-monitoring explanation. Exps 4, 5, and 6 replicated the results of the 1st 3 experiments with predictive inferences. These data provide evidence that predictive inferences, like bridging inferences, are encoded during reading. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Low temperature magnetic circular dichroism spectra of met- and myoglobin derivatives

1. Low temperature magnetic circular dichroism spectra of high and low spin derivatives of metmyoglobin and myoglobin have been measured in the Soret and high wavelength regions. 2. The large difference in intensity of the Soret magnetic circular dichroism bands suggest that a correlation exists between the signal intensity and spin state of the heme-iron. 3. From a comparison of the high and low spin sepctra of the myoglobin derivatives it is concluded that oxymyoglobin contains between 10 and 20% of a ferrous high spin component below 100 degrees K.     

Low frequency vibrational modes in proteins: changes induced by point-mutations in the protein-cofactor matrix of bacterial reaction centers

As a step toward understanding their functional role, the low frequency vibrational motions (<300 cm-1) that are coupled to optical excitation of the primary donor bacteriochlorophyll cofactors in the reaction center from Rhodobacter sphaeroides were investigated. The pattern of hydrogen-bonding interaction between these bacteriochlorophylls and the surrounding protein was altered in several ways by mutation of single amino acids. The spectrum of low frequency vibrational modes identified by femtosecond coherence spectroscopy varied strongly between the different reaction center complexes, including between different mutants where the pattern of hydrogen bonds was the same. It is argued that these variations are primarily due to changes in the nature of the individual modes, rather than to changes in the charge distribution in the electronic states involved in the optical excitation. Pronounced effects of point mutations on the low frequency vibrational modes active in a protein-cofactor system have not been reported previously. The changes in frequency observed indicate a strong involvement of the protein in these nuclear motions and demonstrate that the protein matrix can increase or decrease the fluctuations of the cofactor along specific directions.     

How causal knowledge affects classification: A generative theory of categorization.

Several theories have been proposed regarding how causal relations among features of objects affect how those objects are classified. The assumptions of these theories were tested in 3 experiments that manipulated the causal knowledge associated with novel categories. There were 3 results. The 1st was a multiple cause effect in which a feature's importance increases with its number of causes. The 2nd was a coherence effect in which good category members are those whose features jointly corroborate the category's causal knowledge. These 2 effects can be accounted for by assuming that good category members are those likely to be generated by a category's causal laws. The 3rd result was a primary cause effect, in which primary causes are more important to category membership. This effect can also be explained by a generative account with an additional assumption: that categories often are perceived to have hidden generative causes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Linking theory of mind and central coherence bias in autism and in the general population.

Three experiments investigated whether 2 characteristic aspects of the psychological profile of autism, theory-of-mind deficits and weak central coherence, might be functionally related. Experiment 1 showed that in the general population, performance on a proposed test of theory of mind was inversely related to speed on the Embedded Figures Test, a measure of central coherence bias. Experiments 2 and 3 confirmed that poor theory-of-mind performance was linked to weak central coherence among typically developing children and among children with autism; however, the correlations between these measures were reliable only after accounting for differences in individuals' verbal mental ages. This pattern of results is interpreted in terms of a relationship between individual differences in theory of mind and central coherence bias, a relationship that is separate from any developmental differences in these domains. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Solution hardening in aluminium-magnesium alloys: A nuclear magnetic resonance and transmission electron microscopic study

Pulsed nuclear magnetic resonance techniques as well as transmission electron microscopy have been applied to study dislocation motion in aluminium magnesium alloys (0.2–1.6 at.% Mg). The spin lattice relaxation rate in the rotating frame of ²⁷A1 has been been measured at 77 K as a function of strain at constant plastic strain rate ϵ. For finite strain rates, the movement of dislocations induces an additional relaxation rate arising from time fluctuations in the nuclear quadrupole interactions. From the motion-induced part of the relaxation rate the mean free path of mobile dislocations can be calculated. The NMR experiments are combined with transmission electron microscopic investigations to reveal the static structure of defects in the samples. The NMR measurements clearly indicate that fluctuations in the quadrupolar field caused by moving dislocations in AlMg are different compared to those in ultra pure Al. From the NMR data it could be concluded that moving dislocations advance over a number of solute atoms (order of 7) as described by Mott-Nabarro's model. On the other hand, Mott-Nabarro's model does not predict the effective solute spacing as a function of the concentration of solute atoms in accordance with NMR experiments.